Mobile wireless communication systems currently include base stations, having fixed locations and connections to a core network, and mobile communication devices (also referred to as a “User Equipment” or UE, and/or as “terminals”) that move within the areas covered by the central base stations, and may also move out of the range of central base stations. As the distance increases between user equipment and base stations increases, the transmission power required for error-free communication also increases, until maximum transmission power is reached and no further increase is possible. Beyond this distance, no communication link may be established, and the user equipment is out of range of the base station, and may need to switch to communication through another base station or cell, if one is available. While increasing the transmission power may increase the range of communication, it may also contribute to interference, reducing the signal quality within the coverage area of a base station or cell, as well as in adjacent coverage areas or cells.
Similar problems may arise as an increasing number of user equipment devices communicate with a base station having limited communication resources. In case of a high traffic load within the coverage area of a single base station or cell, the quality of service may be reduced for users, due to inefficient utilization of available resources, or due to the limits of the available communication resources. The communication resources may be determined by, for example, the base station transmission power, the time/frequency/code channels available depending on the multiple access techniques that are used, and/or the interference generated by an increasing number of users.
One approach to increasing the range and capacity of a wireless communication system is addition of new base stations. Unfortunately, new base stations have a number of drawbacks, including the difficulty of selecting suitable locations, establishment of high bandwidth ongoing connections to a core network and the continuous operating costs of maintaining such connections, and (in some cases) resistance encountered from the residents of the area in which the new base station will be established. Overall, the costs and difficulties of adding new base stations to a wireless communication system may make this an undesirable solution.
Another approach to addressing these range and capacity problems is using relay stations, or “multi-hop” networks. In such systems, the term “hop” generally refers to a communication link between two respective network units, for example between a base station and a user equipment device. For example, in a two-hop network, the communication link is, for example between a base station and a relay station, and between the relay station and the user equipment.
Generally, relay stations are similar to a slimmed-down base station that wirelessly receives data from user equipment or from other relay stations, and wirelessly forward such data to other relay stations or to a base station. Such relay stations are often easier to deploy than a base station—they do not generally require a fixed connection to the core network, and have lower operating costs.
In connection with non-cellular systems, numerous mechanisms have been defined for relay stations, which operate in the context of a multi-hop network. For example, IEEE 802.11s defines a WLAN-MESH approach, introducing new user equipment functions, so that user equipment can be used as multi-hop nodes or relay stations. As another example, IEEE 802.16j defines an extension of the WiMAX standard, so that slimmed base stations (i.e., relay stations) can be positioned within respective WiMAX cells. In both of these examples, user equipment is able to communicate indirectly (i.e., via multiple hops) with a base station at a relatively low transmission power level.
One difficulty with these approaches, however, is that they are generally based on the assumption that the user equipment as well as the base station and relay stations are mostly static. Unfortunately, this assumption does not apply in many cases. For example, user equipment can move very rapidly when the user is in a car or train.